ARM: OSIRIS: DVS (Dynamic Voltage Scaling) supoort.

Add a driver to provide DVS for the Simtec Osiris module to reduce
the power consumption whilst idling.

The DVS driver alters the voltage supplied to the ARM core depending
on the frequency it is running at. The driver itself does not do any
of the frequency alteration, which is left up to the cpufreq driver.

Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Simtec Linux Team <linux@simtec.co.uk>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>